According to DC, the hardcover will have a new cover image by J.G. Jones showing "the penultimate scene of the series" (which sounds like a spoiler to me, but what do I know?).
Here's the official press release, via Comic Book Resources:
Official Press ReleaseWhat do you think of the Final Crisis price increase?
DC Comics has expanded the contents of the FINAL CRISIS HC, collecting the explosive event written by Grant Morrison.
Now running 352 pages, this title will include FINAL CRISIS #1-7, FINAL CRISIS: SUBMIT #1 and FINAL CRISIS: SUPERMAN BEYOND #1-2, all written by Morrison, along with a new cover by J.G. Jones depicting the penultimate scene of the series.
The FINAL CRISIS HC (FEB090203) is advance-solicited in the February Previews and is scheduled to arrive in stores on June 10 with a price of $29.99 U.S. Because of these changes, this title will be made returnable at a later date.